Method for inhibiting gas hydrate blockage in oil and gas pipelines

ABSTRACT

This invention relates to a method for inhibiting the agglomeration of gas hydrates, comprising the injection of an anti-agglomerant comprising a N,N-dialkyl-ammoniumalkyl fatty acid amide represented by the formula (I)whereinR1 is an alkyl or alkenyl group having from 7 to 21 carbon atoms,R2 and R3 are each independently an alkyl group containing 1 to 10 carbon atoms, or together form an optionally substituted ring having 5 to 10 ring atoms, wherein the ring may carry up to 3 substituents,R4 is hydrogen or an alkyl group having 1 to 6 carbon atoms,R5 is hydrogen or an optionally substituted hydrocarbyl group having 1 to 22 carbon atoms andA is an alkylene group having two or three carbon atoms,into a fluid comprising gas, water and oil under conditions prone to the formation of gas hydrates,wherein the N,N-dialkyl-ammoniumalkyl fatty acid amide represented by formula (I) is produced by the aminolysis of an ester of a fatty acid and a C1- to C4-alcohol with an N,N-dialkylamino alkyl amine and subsequent neutralization with a carboxylic acid.

The present invention relates to an improved method for inhibiting theformation of gas hydrate plugs in pipelines, transfer lines and otherconduits containing a multiphase mixture comprising water, gas, andcondensate, black oil and/or drilling mud. The method comprises thetreatment of the multiphase mixture with at least one(N,N-dialkyl-ammoniumalkyl) fatty acid amide produced by condensation ofa N,N-dialkylaminoalkylamine with an ester of a fatty acid and amonohydric alcohol. This method provides reduced dosage rates of theadditive. Concurrently the formation of reverse emulsions in downstreamseparators is diminished leading to improved quality of the water phaseto be disposed.

A number of hydrocarbons, especially low molecular weight hydrocarbonswith 1 to 6 carbon atoms, are known to form hydrates in conjunction withwater present in the system under a variety of conditions—particularlyat the combination of lower temperature and higher pressure. In the oiland gas industry such conditions often prevail in equipment that processformation fluids and gases. Usually such hydrates are solids that areessentially insoluble in the fluid itself. Any solids, includinghydrates, present in a formation or natural gas fluid are problematicfor production, handling and transport of these fluids. The solidhydrates may cause plugging and/or blockage of pipelines, transfer linesand other conduits, of valves and/or safety devices and/or otherequipment. This may result in shutdown, lost oil production, pipelinedamage, risk of explosion and/or unintended release of hydrocarbons intothe environment either on-land or off-shore. Therefore, the formation ofgas hydrates poses a safety hazard to field workers and the public. Thedamage resulting from a blockage can be very costly from an equipmentrepair standpoint, as well as from the loss of production, and finallythe resultant environmental impact. Accordingly, gas hydrates are ofsubstantial interest as well as concern to many industries, particularlythe petroleum and natural gas industry.

Gas hydrates are clathrates and are also referred to as inclusioncompounds. Clathrates are cage structures formed between a host moleculeand a guest molecule. A gas hydrate generally is composed of crystalsformed by water host molecules surrounding the hydrocarbon guestmolecules. The smaller and lower-boiling hydrocarbon molecules,particularly C₁-(methane) to C₄ hydrocarbons and their mixtures, areespecially problematic because their hydrate or clathrate crystals areeasy to form. For instance, it is possible for ethane to form hydratesat as high as 4° C. at a pressure of about 1 MPa. If the pressure isabout 3 MPa, ethane hydrates can form at as high a temperature as 14° C.Even certain non-hydrocarbons such as carbon dioxide, nitrogen andhydrogen sulfide are known to form hydrates under certain conditions.Thus, when the appropriate conditions are present, hydrates can easilyform for example during the transportation of moist respectively wet gasin pipelines.

Modern oil and gas technologies tend to operate under increasinglysevere conditions. For example, during drilling operations as well asduring oil recovery and production, high pumping speed, high pressure inthe pipelines, extended length of pipelines, and low temperature of theoil and gas flowing through the pipelines, for example in subseaoperations, are applied. This increases the frequency of formation ofgas hydrates.

There are two basic techniques to overcome or control the gas hydrateproblems, namely thermodynamic and kinetic. For the thermodynamicapproach a number of methods have been reported, including waterremoval, temperature increase, pressure decrease, addition of“antifreeze” to the fluid and/or a combination of these (known in theindustry as Thermodynamic Hydrate Inhibitors and abbreviated THI). Thekinetic approach generally attempts to inhibit and/or to retard initialgas hydrate crystal nucleation and/or further crystal growth (known inthe industry as a Kinetic Hydrate Inhibitor and abbreviated KHI).Thermodynamic and kinetic hydrate control methods may be used inconjunction.

The amount of chemical needed to prevent blockages varies widelydepending upon the type of inhibitor employed. Thermodynamic hydrateinhibitors are substances that can reduce the temperature at which thehydrates form at a given pressure and water content. The most commonlyused classes of THIs are alcohols as for example methanol and ethanol,and glycols as for example ethylene glycol, diethylene glycol andglycerin. They are typically used at very high concentrations (regularlydosed as high as 50 wt.-% based on water content, with ethylene glycoloften being used in amounts equal to the weight of water present in thesystem). Therefore, there is a substantial cost associated with theprovision, transportation and storage of large quantities of thesesolvents. The use of kinetic hydrate inhibitors is a more cost-effectivealternative as they generally require a dose of less than about 2 wt.-%based on the water content to inhibit the nucleation and/or growth ofgas hydrates. Kinetic hydrate inhibitors are often also labeled LowDosage Hydrate Inhibitors (abbreviated LDHI).

Besides the kinetic hydrate inhibitors (KHIs) there is a closely relatedsecond general type of LDHIs, the so-called Anti-Agglomerants(abbreviated AA). While KHIs work by delaying the growth of gas hydratecrystals and may function as “anti-nucleators”, AAs allow hydrates toform but prevent them from agglomerating and subsequently fromaccumulating into larger aggregates capable of causing plugs. Often AAsprevent the once formed smaller gas hydrate crystals to adhere to thepipe wall.

Kinetic efforts to control hydrates have included the use of differentchemicals as inhibitors. Typically, KHIs are low molecular weightpolymers that adsorb on gas hydrate crystal faces and interfere with thenucleation and growth of gas hydrate crystals. For instance, polymerscomprising lactam rings (stemming e.g. from vinyl caprolactam) have beenemployed to control clathrate hydrates in fluid systems. Similarly,onium compounds with at least four carbon substituents are used toinhibit the plugging of conduits by gas hydrates. Unfortunately, thereare several limitations that have been discovered with the use of KHIssuch as subcooling limits, solubility problems based on temperature andsalt content of the water, and chemical incompatibility with the systembeing treated.

Anti-agglomerants typically are surface active molecules (amphiphiles).Without wishing to be bound to this theory, it has been hypothesizedthat when small gas hydrate crystals begin to form, AAs attach to themvia their polar headgroup. This makes the surface hydrophobic, whichmediates the capillary attraction between the crystals and water andfosters dispersion of the crystals in a liquid hydrocarbon phase. Thisresults in a relatively stable and transportable hydrate slurry in aliquid hydrocarbon phase that can flow to the processing facility. AAsare usually added at dose rates of less than 0.5 wt.-% and up to 2.0wt.-% based on the water phase.

Besides some polymeric substances and especially nitrogen-containingpolymers many different monomeric substances have been described to workas anti-agglomerant. Quaternary amine chemistry has been proven to beespecially effective as anti-agglomerant for hydrate control. The bestperforming AAs are quaternary ammonium surfactants in which the ammoniumheadgroup has two or three butyl or pentyl groups attached to thequaternary nitrogen.

A variety of approaches to optimize the performance of anti-agglomerantsby modifying the structure of hydrophilic and lipophilic groups andtheir balance have been made.

GB 2349889 discloses a method for inhibiting the formation andagglomeration of gas hydrates in a fluid containing hydrate formingconstituents by adding to the hydrate forming fluids an additivecomprising one or more amide compounds of molecular weight less than1.000.

WO 2005/042675 discloses a method and an amide composition used thereinfor inhibiting, retarding, mitigating, reducing, controlling and/ordelaying the formation of gas hydrates or agglomerates of gas hydrates.The disclosure encompasses the amides obtained by reaction of anN,N-dialkyl-aminoalkylamine with an ester or glyceride as for example avegetable oil or tallow oil and subsequent reaction with a reactantselected from an alkyl halide, hydrogen peroxide and an acid selectedfrom mineral acids and specific carboxylic acids.

WO 2013/048365 discloses an anti-agglomerate hydrate inhibitorcomposition, comprising a reaction product of an organic amine and anacid selected from the group consisting of non-halide-containinginorganic acids and organic acids, and mixtures thereof, wherein thereaction product is substantially free of halides containing compounds.The halide free AA-LDHI compositions are not as corrosive as the likesof HCl or HX, do not cause halide stress cracking, and are not as toxic.

WO 2017/105507 discloses high temperature hydrate inhibitors and methodsof using such compositions to inhibit the formation of gas hydrateagglomerates. The inhibitor comprises an amide obtained by reaction ofN,N-dialkyl-aminopropylamine with one or more fatty acids or fatty acidesters and subsequent neutralization with an organic sulfonate, e.g.methane sulfonic acid, respectively quaternization with an organicsulfate, e.g. diethylsulfate. These LDHIs are halogen free and may beexposed to temperatures above 200° F. (93° C.) for an extended period oftime without substantially degrading.

WO 2018/115186 discloses a method for inhibiting the formation of gashydrates in systems comprising mixture of hydrocarbons and water,comprising the addition of an alkyl sulfate or alkyl carbonate orcarbonate salt of a quaternary ammonium amide with a relatively shortfatty chain.

However, upon application of quaternary ammonium surfactants, theseparation of the multiphase fluids and the water quality obtainedthereby are industrial-wide technical challenges, therefore thwartingits broad field implementation to replace conventional THI methods.Often anti-agglomerants cause reverse emulsion problems in separatorstopside. This includes both free droplets of oil in water and condensedmesophases at the interface comprising surface active salts ofnaphthenic acids from the oil phase. Thus, there is the desire for LDHIswhich give an improved water quality upon separation of the multiphasemixture comprising oil, gas and water phase under conditions no longerprone to hydrate formation, e.g. prior to further processing of the gasand oil phases. Besides easier disposal of the separated water phasethis will concurrently raise the production rate of oil and gas. Anotherdrawback of current anti-agglomerants is their high viscosity.Anti-agglomerants are usually injected at the wellhead or even into theformation. Especially in deepwater applications this often requirestransportation in tight umbilicals over long distances at lowtemperatures of about 4° C. or below which necessitates high dilution ofthe additive and/or high pumping power. Accordingly, there is a demandfor anti-agglomerants with a reduced viscosity which allow for lowerpumping power and/or higher concentration of the anti-agglomerant.Furthermore, it is desirable if new gas hydrate inhibitors werediscovered which yield improved performance over known gas hydrateinhibitors. Accordingly, there is a constant strive for more efficientLDHIs which require lower dosage rates while maintaining effectivehydrate inhibition. Similarly, there is an ambition for new syntheticroutes for gas hydrate inhibitors having improved economics.

Accordingly, there is an ongoing need for compositions and methods thateffectively prevent agglomeration of gas hydrates especially in oil andgas transportation and handling processes. Particularly there is a needfor anti-agglomerants which need lower dosage rates to ensure effectivehydrate inhibition. Similarly, there is a need for anti-agglomerantswhich allow for improved handling especially in deepwater applications,i.e. which have a reduced viscosity. Furthermore, a means to mitigatethe environmental impact of the use of a gas hydrate inhibitor byimprovement of the water quality obtained upon separation of themultiphase mixture into its components is sought.

Surprisingly it was found that salts of N,N-dialkyl-ammoniumalkyl fattyacid amides as described in WO 2005/042675 prevent gas hydrateagglomeration more effectively when produced fromN,N-dialkylaminoalkylamine and an ester of a fatty acid with amonohydric alcohol having 1 to 4 carbon atoms. Furthermore, uponseparation of the multiphase mixture into its components there is onlylittle or even no formation of reverse emulsion of oil in the waterphase and the interface shows only little or even no emulsion.Surprisingly solutions of the anti-agglomerants produced according tothe invention have a reduced viscosity especially at low temperatures.

Accordingly, in a first aspect of the invention there is provided amethod for inhibiting the agglomeration of gas hydrates, comprising theaddition of an anti-agglomerant comprising a N,N-dialkyl-ammoniumalkylfatty acid amide represented by the formula (I)

wherein

-   -   R¹ is an alkyl or alkenyl group having from 7 to 21 carbon        atoms,    -   R² and R³ are each independently an alkyl group containing 1 to        10 carbon atoms, or together form an optionally substituted ring        having 5 to 10 ring atoms, wherein the ring may carry up to 3        substituents,    -   R⁴ is hydrogen or an alkyl group having 1 to 6 carbon atoms,    -   R⁵ is hydrogen or an optionally substituted hydrocarbyl group        having 1 to 22 carbon atoms and    -   A is an alkylene group having two or three carbon atoms,

to a mixture comprising gas, water and oil under conditions prone to theformation of gas hydrates,

wherein the N,N-dialkyl-ammoniumalkyl fatty acid amide represented bythe formula (I) is produced by the aminolysis of an ester of a fattyacid and a monohydric alcohol having 1 to 4 carbon atoms, with anN,N-dialkylamino alkyl amine and subsequent neutralization with acarboxylic acid.

In a second aspect of the invention there is provided the use of ananti-agglomerant comprising a N,N-dialkyl-ammoniumalkyl fatty acid amiderepresented by the formula (I)

wherein

-   -   R¹ is an alkyl or alkenyl group having from 7 to 21 carbon        atoms,    -   R² and R³ are each independently an alkyl group containing 1 to        10 carbon atoms, or together form an optionally substituted ring        having 5 to 10 ring atoms, wherein the ring may carry up to 3        substituents,    -   R⁴ is hydrogen or an alkyl group having 1 to 6 carbon atoms,    -   R⁵ is hydrogen or an optionally substituted hydrocarbyl group        having 1 to 22 carbon atoms and    -   A is an alkylene group having two or three carbon atoms,

for inhibiting the agglomeration of gas hydrates in a mixture comprisinggas, water and oil under conditions prone to the formation of gashydrates,

wherein the N,N-dialkyl-ammoniumalkyl fatty acid amide represented bythe formula (I) is produced by the aminolysis of an ester of a fattyacid and a monohydric alcohol having 1 to 4 carbon atoms, with anN,N-dialkylamino alkyl amine and subsequent neutralization with acarboxylic acid.

In a third aspect of the invention there is provided a fluid containinggas, water, and oil and a gas hydrate anti-agglomerant comprising aN,N-dialkyl-ammoniumalkyl fatty acid amide represented by the formula(I)

wherein

-   -   R¹ is an alkyl or alkenyl group having from 7 to 21 carbon        atoms,    -   R² and R³ are each independently an alkyl group containing 1 to        10 carbon atoms, or together form an optionally substituted ring        having 5 to 10 ring atoms, wherein the ring may carry up to 3        substituents,    -   R⁴ is hydrogen or an alkyl group having 1 to 6 carbon atoms,    -   R⁵ is hydrogen or an optionally substituted hydrocarbyl group        having 1 to 22 carbon atoms and    -   A is an alkylene group having two or three carbon atoms,

wherein the N,N-dialkyl-ammoniumalkyl fatty acid amide represented bythe formula (I) is produced by the aminolysis reaction of an ester of afatty acid and a monohydric alcohol having 1 to 4 carbon atoms, with anN,N-dialkylamino alkyl amine and subsequent neutralization with acarboxylic acid.

In the context of this invention the terms hydrate, hydrocarbon hydrate,gas hydrate and clathrate all refer to solid hydrates of low molecularweight hydrocarbons and water and are used synonymously. The termsanti-agglomerant and gas hydrate anti-agglomerant are used synonymouslyand refer to substances which inhibit the agglomeration of gas hydrates.The term “inhibiting the agglomeration of gas hydrates” encompassesinhibiting, retarding, reducing, controlling, and/or delaying theformation of hydrates and/or the agglomeration of hydrate crystals.

The N,N-dialkyl-ammoniumalkyl fatty acid amides (I) used in thedifferent aspects of the invention are obtained by the aminolysis of anester of a fatty acid and a monohydric alcohol having 1 to 4 carbonatoms, with a N,N-dialkylaminoalkylamine and subsequent reaction of theintermediate amido amine with a carboxylic acid.

Fatty Acid Ester

Preferred fatty acid esters as starting material for the production ofN,N-dialkyl-ammoniumalkyl fatty acid amides (I) are esters having theformula (III)R¹—COOR⁶  (III)

wherein

-   -   R¹ is an alkyl or alkenyl group having from 7 to 21 carbon atoms        and    -   R⁶ is an alkyl residue having 1 to 4 carbon atoms.

In a preferred embodiment R¹ is an alkyl or alkenyl group having from 9to 17 carbon atoms and especially preferred having from 11 to 13 carbonatoms, as for example from 9 to 21, or from 9 to 13, or from 7 to 17, orfrom 7 to 13, or from 11 to 21, or from 11 to 17 carbon atoms. Preferredalkyl groups R¹ may be linear or branched. More preferably they arelinear. Preferred alkenyl groups R¹ may have one or more C═C doublebonds as for example one or two C═C double bonds.

Preferably, fatty acid esters (III) are derivatives of fatty acidshaving the formula (IV)R¹—COOH  (IV)

wherein R¹ has the meaning given above. Examples for preferred fattyacids (IV) are octanoic acid, 2-ethylhexanoic acid, nonanoic acid,iso-nonanoic acid, decanoic acid, neodecanoic acid, undecanoic acid,neoundecanoic acid, dodecanoic acid, dodecenoic acid, neododecanoicacid, tridecanoic acid, iso-tridecanoic acid, tetradecanoic acid,tetradecenoic acid, pentadecanoic acid, hexadecanoic acid, octadecanoicacid, oleic acid and their mixtures. Especially preferred fatty acidsare dodecanoic acid, tetradecanoic acid and their mixtures.

In a preferred embodiment an ester (III) which is based on a mixture offatty acids (IV) is used. Mixtures of fatty acids (IV) may contain forexample acids with different chain lengths, with different degrees ofunsaturation and/or with different degrees of branching. In preferredfatty acid mixtures at least 60 mol-%, more preferably at least 75mol-%, most preferred at least 85 mol-% and especially preferred atleast 90 mol-% of the alkyl and/or alkenyl residues R¹ as for example 60to 99 mol-%, or 60 to 95 mol-%, or 75 to 99 mol-%, or 75 to 95 mol-%, or85 to 99 mol-%, or 85 to 90 mol-%, or 90 to 99 mol-%, or 90 to 95 mol-%of the fatty acids of formula (IV) have 12 to 14 carbon atoms. In afurther preferred embodiment the molar ratio of fatty acids having 12carbon atoms and fatty acids having 14 carbon atoms is between 20:1 and1:20, more preferably between 10:1 and 1:10 and especially preferredbetween 8:1 and 1:1. In a preferred embodiment the fatty acids having 12to 14 carbon atoms are linear or at least essentially linear, i.e.preferably at least 60 mol-% and more preferably at least 80 mol-% andespecially at least 90 mol-% of the fatty acids are linear.

The fatty acids (IV) may be of natural or synthetic origin. Especiallypreferred are mixtures of fatty acids derived from renewable materialsas for example palm fatty acid, coco fatty acid, soya fatty acid, sunflower fatty acid, rapeseed fatty acid and tallow fatty acid andincluding the respective fatty acid distillates. Such fatty acids andfatty acid mixtures are readily available in the market. The fatty acidmixtures derived from natural sources may be used as such or uponhydrogenation respectively partial hydrogenation. Preferred fatty acidsand fatty acid mixtures (IV) have acid numbers determined according toDIN/EN/ISO 2114 of at least 50 mg KOH/g, more preferably between 100 and390 mg KOH/g and especially preferred between 120 and 320 mg KOH/g asfor example between 50 and 390 mg KOH/g, or between 50 and 320 mg KOH/g,or between 100 and 320 mg KOH/g, or between 120 and 390 mg KOH/g. Theacid numbers may be determined according to DIN/EN/ISO 2114.

The ester used for production of N,N-dialkyl-ammoniumalkyl fatty acidamides (I) is an ester of the fatty acid (IV) with a monohydric C₁- toC₄-alcohol. Preferred monohydric alcohols are methanol, ethanol,n-propanol, iso-propanol, n-butanol, iso-butanol, tert.-butanol andtheir mixtures. Especially preferred are methyl esters.

Examples for preferred esters are octanoic acid methyl ester,2-ethylhexanoic acid methyl ester, nonanoic acid methyl ester,iso-nonanoic acid methyl ester, decanoic acid methyl ester, neodecanoicacid methyl ester, undecanoic acid methyl ester, neoundecanoic acidmethyl ester, dodecanoic acid methyl ester, dodecenoic acid methylester, neododecanoic acid methyl ester, tridecanoic acid methyl ester,iso-tridecanoic acid methyl ester, tetradecanoic acid methyl ester,tetradecenoic acid methyl ester, pentadecanoic acid methyl ester,hexadecanoic acid methyl ester, octadecanoic acid methyl ester, behenicacid methyl ester, oleic acid methyl ester, the respective ethyl,n-propyl, iso-propyl, n-butyl, and iso-butyl esters and their mixtures.Especially preferred fatty acid esters are dodecanoic acid methyl ester,tetradecanoic acid methyl ester and their mixtures. Especially preferredesters based on natural fats are coconut methyl ester, hydrogenatedcoconut methyl ester, coconut ethyl ester and palm kernel methyl ester.

The description of the esters used for production ofN,N-dialkyl-ammoniumalkyl fatty acid amides (I) given above is based onthe fatty acid they are based on. However, this is to be understood as acharacterization of the alkyl chain length respectively the alkyl chainlength distribution of fatty acid component of the ester. Besides it'ssynthesis by esterification of the respective fatty acid (IV) with theC₁- to C₄-alcohol the ester may also be synthesized by other proceduresknown to the person skilled in the art, as for example bytransesterification of a triglyceride with the C₁- to C₄-alcohol.

N,N-Dialkylaminoalkylamine

Preferred N,N-dialkylaminoalkylamines as starting material for theproduction of N,N-dialkyl-ammoniumalkyl fatty acid amides (I) have thegeneral formula (V)

wherein

-   -   R² and R³ are each independently an alkyl group containing 1 to        10 carbon atoms, or together form an optionally substituted ring        having 5 to 10 ring atoms, wherein the ring may carry up to 3        substituents,    -   R⁴ is hydrogen or an alkyl group having 1 to 6 carbon atoms and    -   A is an alkylene group having two or three carbon atoms.

In a preferred embodiment R² and R³ are each independently from anotheran alkyl group having 2 to 6 carbon atoms, more preferably having 3 to 5carbon atoms and especially preferred having 3 or 4 carbon atoms, as forexample having 1 to 6 carbon atoms, or 1 to 5 carbon atoms, or 1 to 4carbon atoms, or 2 to 10 carbon atoms, or 2 to 5 carbon atoms, or 2 to 4carbon atoms, or 3 to 10 carbon atoms, or 3 to 6 carbon atoms. Examplesfor preferred alkyl groups R² and R³ are methyl, ethyl, propyl,iso-propyl, n-butyl, iso-butyl, tert.-butyl, and the various isomers ofpentyl, hexyl, heptyl, octyl, nonyl and decyl. Especially preferred arelinear alkyl groups. R² and R³ may be different or they may be the same.In a preferred embodiment R² and R³ both have 3 to 5 carbon atoms. In afurther preferred embodiment R² and R³ both are linear alkyl groups. Ina most preferred embodiment R² and R³ both are linear C₃-, C₄-, orC₅-alkyl groups.

In a further preferred embodiment R² and R³ together form a ring having5 to 8 and especially preferred having 5 or 6 ring atoms, including thenitrogen atom carrying the residues R² and R³. Preferably the furtherring atoms are carbon atoms. In a further preferred embodiment the ringcomprises, besides carbon atoms, one or two ring atoms selected from N,O and S. Examples for preferred cyclic structures are 1-piperidyl,pyrrolidin-1-yl, piperazin-1-yl and morpholinyl residues. The ringformed by R² and R³ may be substituted with one, two or threesubstituents. In a preferred embodiment the ring carries onesubstituent. Preferred substituents are alkyl residues having 1 to 4carbon atoms as for example methyl, ethyl, n-propyl, isopropyl, n-butyl,isobutyl and tert.-butyl groups. The substituent may be bound to acarbon atom. Preferably it is bound to a nitrogen atom, if present.

A is an alkylene group having two or three carbon atoms. Preferably A isan ethylene or a propylene group. When A has 3 carbon atoms it may bestraight-chain or branched. In a more preferred embodiment A is anethylene group having the formula —CH₂—CH₂— and in an especiallypreferred embodiment A is a propylene group having the formula—CH₂—CH₂—CH₂—.

Preferably R⁴ is hydrogen or an alkyl group having 1 to 4 carbon atomsas for example a methyl, ethyl, propyl, isopropyl, butyl, isobutyl orter.-butyl group. Especially preferred R⁴ is hydrogen.

Examples for preferred N,N-dialkylaminoalkyleneamines according toformula (V) are N,N-dimethylaminoethylamine,N,N-dimethylaminopropylamine, N,N-diethylaminoethylamine,N,N-diethylaminopropylamine, N,N-dipropylaminoethylamine,N,N-dipropylaminopropylamine, N,N-dibutylaminoethylamine,N,N-dibutylaminopropylamine and N,N-dimethylamino-2-hydroxypropylamine,N-(3-aminopropyl)pyrrolidine, N-(3-aminopropyl)piperidine,1-(3-aminopropyl)-piperazine and 1-(3-aminopropyl)-4-methylpiperazine.The preparation of N,N-dialkylaminoalkylenamines is described forexample in Journal of the American Chemical Society 1944, 66(5),725-731.

In a first reaction step the fatty acid ester (III) andN,N-dialkylaminoalkylamine (V) are reacted to give the correspondingN,N-dialkylaminoalkylamino fatty acid amide (II).

wherein R¹, R², R³, R⁴, R⁶ and A have the meanings given above.

In a subsequent reaction step the intermediate N,N-dialkylaminoalkylfatty acid amide (II) is reacted with a carboxylic acid (VI) to give theN,N-dialkyl-ammoniumalkyl fatty acid amide (I).

wherein R¹, R², R³, R⁴, R⁵ and A have the meanings given above.

Carboxylic Acid

Preferred carboxylic acids for the reaction with the intermediate amidoamine (II) have the formula (VI)R⁵—COOH  (VI)

wherein R⁵ is hydrogen or an optionally substituted hydrocarbyl residuehaving between 1 and 17 carbon atoms, preferably between 2 and 11 carbonatoms and especially preferred between 2 and 5 carbon atoms as forexample between 1 and 11 carbon atoms, or between 1 and 5 carbon atoms,or between 2 and 17 carbon atoms.

In preferred carboxylic acids according to formula (VI) the optionallysubstituted hydrocarbyl residue R⁵ is an alkyl or alkenyl residue withalkenyl residues having at least two carbon atoms. Preferred alkyl andalkenyl residues may be linear or, having three or more carbon atoms,may be branched. Preferred alkenyl residues R⁵ have one or more as forexample one, two or three double bonds. Preferred substituents arehydroxy groups, carboxylic acid groups and amino groups. Preferredcarboxylic acids (VI) include natural and synthetic fatty acids.Carboxylic acids based on renewable raw materials are especiallypreferred. Such fatty acids are obtainable for example by saponificationof naturally occurring oils and fats and optionally furtherderivatization.

Examples for preferred carboxylic acids R⁵—COOH (VI) are formic acid,acetic acid, propionic acid, butyric acid, pivalic acid, hexanoic acid,octanoic acid, 2-ethyl hexanoic acid, decanoic acid neodecanoic acid,undecanoic acid, neoundecanoic acid, dodecanoic acid, neododecanoicacid, tridecanoic acid, iso-tridecanoic acid, tetradecanoic acid,hexadecanoic acid, octadecanoic acid, acrylic acid, methacrylic acid andtheir mixtures. Mixtures of carboxylic acids may contain acids withdifferent chain lengths, with different degrees of unsaturation and/ordifferent degrees of branching. Especially preferred are mixtures ofcarboxylic acids based on natural fats and oils as for example cocofatty acid, rape seed fatty acid, soya fatty acid, palm fatty acid, palmkernel fatty acid, tallow fatty acid, and tall oil fatty acid. Thesecarboxylic acid mixtures may be used as such or upon hydrogenationrespectively partial hydrogenation. In a preferred embodiment R⁵ is asaturated C₁- to C₁₇ alkyl residue and especially preferred a saturatedC₁- to C₅ alkyl residue. In a further especially preferred embodiment R⁵is an unsaturated C₂- to C₅ alkenyl residue. Examples for especiallypreferred carboxylic acids are acrylic acid, methacrylic acid, aceticacid, propionic acid, dodecanoic acid and coconut fatty acid. The fattyacid used in the first reaction step and the carboxylic acids use in thesecond reaction step may be the same or different.

In a preferred embodiment most of the starting fatty acid and/or thecarboxylic acid are selected from renewable materials. In an especiallypreferred embodiment all or at least essentially all of the startingfatty acid and/or the carboxylic acid are selected from renewablematerials. Accordingly, the hydrate inhibitors according to theinvention are considered to be renewable.

Synthesis

For production of the intermediate N,N-dialkylaminoalkyl fatty acidamide (II) the fatty acid ester (III) maybe reacted with theN,N-dialkylaminoalkylamine (V) at a temperature of between 100 and 240°C., preferably at a temperature of between 120 and 200° C., as forexample between 100 and 200° C. or between 120 and 240° C. Theaminolysis reaction is suitably effected by heating the mixture for aperiod of from 2 to 20 hours. The pressure is preferably between 0.001and 10 bar and more preferred between 0.01 and 3.0 bar. Preferably thealcohol formed during the aminolysis reaction is removed viadistillation. The degree of reaction can be followed by determination ofthe saponification number and/or by the determination of the aminefunctionality distribution. In a preferred embodiment the condensationto the corresponding N,N-dialkylaminoalkyl fatty acid amide (II) isconducted until no further alcohol is formed. This indicates a completeor an essentially complete conversion.

In the aminolysis reaction step preference is given to using essentiallyequimolar quantities of fatty acid ester (III) andN,N-dialkylaminoalkylamine (V). Essentially equimolar proportionsinclude molar ratios between fatty acid ester (III) andN,N-dialkylaminoalkylamine (V) of between 3:1 and 1:3, more preferablybetween 1.5:1 and 1:1.5 and especially preferred between 1.1:1 and1:1.1, as for example between 3:1 and 1:1.5, or between 3:1 and 1:1.1,or between 1.5:1 and 1:3, or between 1.5:1 and 1:1.1, or between 1.1:1and 1:3 or between 1.1:1 and 1:1.5.

During the aminolysis reaction the monohydric C₁ to C₄-alcohol isreleased as a by-product. In order to drive the reaction to completionthe alcohol may be distilled off. However, in certain embodiments thealcohol may remain in the product.

The aminolysis reaction can be accelerated by addition of suitablecatalysts. Catalysts having a pKa of less than or equal to 5 arepreferred, with Bronstedt and Lewis bases being especially preferred.Examples for preferred catalysts are hydroxides and alkoxides includingbut not limited to sodium hydroxide, potassium hydroxide, sodiummethoxide, sodium ethoxide, potassium methoxide, potassiumtert.-butoxide, triethylamine, morpholine, and pyridine. Typically 0.01to 1 wt.-% and preferably 0.1 to 0.5 wt.-% of the catalyst in respect tothe combined masses of the N,N-dialkylaminoalkylamine (V) and the fattyacid ester (III) are used. In a first preferred embodiment the catalystremains in the reaction product. Accordingly, the N,N-dialkylaminoalkylfatty acid amide (II) may contain up to 1.5 mol-% and especiallypreferred less than 0.5 mol-% of the catalyst in respect to theN,N-dialkylaminoalkyl fatty acid amide (II). In a second preferredembodiment the catalyst is removed from the amide reaction product afterthe reaction, e.g. by extraction. In a third preferred embodiment thereaction is made in absence of a catalyst. Accordingly, in the secondand third preferred embodiments the N,N-dialkylaminoalkyl fatty acidamide (II) does not contain any catalyst and especially no alkaline.

For production of the N,N-dialkylammoniumalkyl fatty acid amide (I) theintermediate N,N-dialkylaminoalkyl fatty acid amide (II) is reacted withthe carboxylic acid (VI). Preferably, salt formation is accomplished bymixing the N,N-dialkylaminoalkyl fatty acid amide (II) with anappropriate amount of the carboxylic acid (VI) to give the correspondingN,N-dialkylammoniumalkyl fatty acid amide salt (I). Preferably theformation of the salt is made at temperatures between ambient and 100°C. and more preferably at temperatures between 30 and 60° C. Preferablythe carboxylic acid (VI) is added to the N,N-dialkylaminoalkyl fattyacid amide (II) in a manner that the temperature does not exceed 100° C.and more preferably not 70° C. Preferably the carboxylic acid (VI) andthe N,N-dialkylaminoalkyl fatty acid amide (II) are reacted in a molarratio of between 1:10 and 5:1, more preferably between 1:5 and 3:1 andespecially preferred between 1:2 and 1:1, as for example between 1:10and 3:1, or between 1:10 and 1:1, or between 1:5 and 5:1, or between 1:5and 1:1, or between 1:2 and 5:1, or between 1:2 and 3:1. In a specificembodiment carboxylic acid (VI) and N,N-dialkylaminoalkyl fatty acidamide (II) are reacted in equimolar or at least essentially equimolarquantities as for example between 1:1.5 and 1.5:1 or between 1:1.2 and1.2:1. The given molar ratios refer to the number of carboxylic acidgroups of the carboxylic acid (VI) and to the amino groups of theN,N-dialkylaminoalkyl fatty acid amide (II).

The reaction sequence can be executed solvent free. However, in manycases it has proven to be advantageous to conduct the reaction or atleast one or more of the reaction steps in the presence of a solvent.Especially for the reaction of the fatty acid ester (III) with theN,N-dialkylaminoalkylamine (V) the presence of a solvent is preferredwhen a high conversion to the resulting reaction product is targeted.Preferred solvents for the reaction are aromatic solvents or solventmixtures, or alcohols. Particular preference is given to solvents havinga boiling point of at least 100° C. and preferably 110 to 200° C. understandard conditions. Examples of suitable solvents are decane, toluene,xylene, diethylbenzene, naphthalene, tetralin, decalin, and commercialsolvent mixtures such as Shellsol®, Exxsol®, Isopar®, Solvesso® types,Solvent Naphtha and/or kerosene. In a preferred embodiment, the solventcomprises at least 10% by weight, preferably 20 to 100% by weight, forexample 30 to 90% by weight, of aromatic constituents. Shellsol® andExxsol® grades are obtainable form Shell and ExxonMobil, respectively.The reaction is then effected at the boiling point of the azeotrope.

The thus produced N,N-dialkylammoniumalkyl fatty acid amide salt (I) maybe purified by any methods known to the skilled in the art, e.g, byfiltration, extraction, distillation or recrystallization. However, inmost cases the direct reaction product has proven to be suited fordirect application.

The anti-agglomerants of the present disclosure may be used to inhibit,retard, mitigate, reduce, control, and/or delay the formation of one ormore hydrates or agglomerates of hydrates. In a preferred embodiment oneor more anti-agglomerants of the present disclosure may be introducedinto a fluid comprising water, a gas and a liquid hydrocarbon. Althoughlisted separately from liquid hydrocarbon, the gas may in someembodiments include gaseous hydrocarbon, though the gas need notnecessarily include hydrocarbon.

The fluids to be inhibited from gas hydrate agglomeration may havedifferent water cuts (i.e., the ratio of the volume of water in thefluid to the total volume of the fluid). For example, theanti-agglomerants according to the disclosure of the invention have beensuccessfully applied in fluids having a water cut of about 1 to about 65vol.-%. In preferred embodiments, a fluid may have a water cut of 1% ormore, 5% or more, 10% or more, 15% or more, 20% or more, 30% or more,40% or more, 50% or more, or 60% or more.

The method according to the first aspect of the invention and the useaccording to the second aspect of the invention are especiallyadvantageous in neutral and especially in acidic fluids, i.e. fluidshaving a pH of below 8.0, more preferably of below 7.5, still morepreferably of below 7.0 and especially preferred of below 6.5.

In a preferred embodiment the fluid to be inhibited from gas hydrateagglomeration is a petroleum fluid being the mixture of varying amountsof water/brine, crude oil/condensate, and natural gas. The petroleumfluid may contain various levels of salinity. The fluid can have asalinity of about 0% to about 25% or about 10% to about 25%weight/weight (w/w) total dissolved solids (TDS).

The petroleum fluids in which the gas hydrate anti-agglomerant isapplied according to the first and second aspect of the invention can becontained in many different types of apparatuses, especially those thattransport an aqueous medium from one location to another. In a preferredembodiment the petroleum fluid is contained in an oil and gas pipeline.In a further preferred embodiment the petroleum fluid to be treated canbe contained in refineries, such as separation vessels, dehydrationunits, gas lines, and pipelines.

For inhibition of gas hydrate agglomeration according to the first andsecond aspect of the invention the N,N-dialkylammoniumalkyl fatty acidamide salt (I) is injected into the fluid to be inhibited from gashydrate agglomeration. Preferably, the hydrate anti-agglomerant isinjected into the fluid to be inhibited prior to substantial formationof hydrates. The anti-agglomerant may be introduced into the fluidthrough a conduit or an injection point. In certain embodiments, one ormore anti-agglomerants of the present disclosure may be introduced intoa wellbore, a conduit, a vessel, and the like and may contact and/or beintroduced into a fluid residing therein. An exemplary injection pointfor petroleum production operations is downhole near the surfacecontrolled sub-sea safety valve. This ensures that during a shut-in, thegas hydrate anti-agglomerant is able to disperse throughout the areawhere hydrates will occur. Treatment can also occur at other areas inthe wellhead or flowline manifold or the flowline itself, taking intoaccount the density of the injected fluid. If the injection point iswell above the hydrate formation point, then the hydrateanti-agglomerant can be formulated with a solvent having a density highenough that the inhibitor will sink in the flowline to collect at thewater/oil interface. Moreover, the treatment can also be used inpipelines or anywhere in the system where the potential for hydrateformation exists.

The method according to the first aspect of the invention and the use ofthe anti-agglomerant according to the second aspect of the invention areequally applicable for fluids which are flowing as well as for fluidswhich are substantially stationary. Accordingly, the fluid may be withina vessel, or within a conduit (e.g., a conduit that may transport thefluid), or within a subterranean formation and/or a wellbore penetratinga portion of the subterranean formation. Examples of conduits include,but are not limited to, pipelines, production piping, subsea tubulars,process equipment, and the like as used in industrial settings and/or asused in the production of oil and/or gas from a subterranean formation,and the like. The conduit may in certain embodiments penetrate at leasta portion of a subterranean formation, as in the case of an oil and/orgas well. In particular embodiments, the conduit may be a wellbore ormay be located within a wellbore penetrating at least a portion of asubterranean formation. Such oil and/or gas well may, for example, be asubsea well (e.g., with the subterranean formation being located belowthe sea floor), or it may be a surface well (e.g., with the subterraneanformation being located belowground). A vessel or conduit according toother embodiments may be located in an industrial setting such as arefinery (e.g., separation vessels, dehydration units, pipelines, heatexchangers, and the like), or it may be a transportation pipeline.

The gas hydrate anti-agglomerant according to the invention ispreferably used in amounts of between 0.01 and 5.0% by weight (based onthe weight of the aqueous phase), more preferably in amounts between0.05 and 3.0 wt.-% and especially preferred in amounts between 0.1 and1.0 wt.-%, as for example between 0.01 and 3.0 wt.-%, or between 0.01and 1.0 wt.-%, or between 0.05 and 5.0 wt.-%, or between 0.05 and 1.0wt.-%, or between 0.1 and 5.0 wt.-% or between 0.1 and 3.0 wt.-%. Itwill be appreciated by one of ordinary skill in the art that the amountof the anti-agglomerant according to the present invention effective forinhibiting, retarding, reducing, controlling, delaying the formationand/or the agglomeration of hydrates may depend upon, for example, thevolume of water in the fluid and/or further additives in the fluid to betreated.

The anti-agglomerants according to the disclosure may be used solely aswell as in a formulation containing a solvent and/or further activeswhich further inhibit the formation of hydrates.

In a first preferred embodiment of the first and second aspect of theinvention mixtures of two or more of the anti-agglomerants according tothe disclosure of this invention are used. Such mixtures may include twoor more N,N-dialkylammoniumalkyl fatty acid amide salts of formula (I)differing in at least one feature of R¹, R², R³, R⁴, and/or A, forexample in the alkyl or alkenyl group R¹ of the fatty acid.

In a second preferred embodiment of the first and second aspect of theinvention the N,N-(dialkylammoniumalkyl)carboxylic acid amide salt (I)is used in combination with a N,N-(dialkylaminoalkyl)carboxylic acidamide (II). Such formulation may be obtained by mixing of the individualcomponents. Alternatively, such mixture may be obtained by partialneutralization of the N,N-dialkylaminoalkyl fatty acid amide (II) withthe carboxylic acid (VI). Preferably the portions of both species (II)and (I) in such mixtures are between 100:1 and 1:100, more preferablybetween 20:1 and 1:20, more preferably between 10:1 and 1:10 andespecially preferred between 5:1 and 1:2 as for example between 100:1and 1:20, or between 100:1 and 1:10, or between 100:1 and 1:2, orbetween 20:1 and 1:100, or between 20:1 and 1:10, or between 20:1 and1:2, or between 10:1 and 1:100, or between 10:1 and 1:20, or between10:1 and 1:2, or between 5:1 and 1:100, or between 5:1 and 1:20, orbetween 5:1 and 1:10.

In the first and second preferred embodiment above the mixtures ofanti-agglomerants are used with the same preferred overall dosage ratesas disclosed above for a single anti-agglomerant according to thedisclosure. However, often such mixtures allow for a reduction of theoverall dosage rate.

In a third preferred embodiment of the first and second aspect of theinvention, the anti-agglomerants according to the disclosure of theinvention are used as a formulation in an organic solvent. Thisfacilitates the handling of the inhibitors and furthermore it oftensupports dispersion of the hydrate crystals. In a first embodiment analcoholic solvent such as a water-soluble monoalcohol, for examplemethanol, ethanol, propanol, butanol, an oxyethylated monoalcohol suchas butyl glycol, isobutyl glycol, butyl diglycol, a polyglycol, or amixture thereof is particularly preferred. In a further preferredembodiment, a hydrocarbon containing a carbonyl group such as a ketone,for example acetone, methyl ethyl ketone (2-butanone), methyl propylketone, methyl isopropyl ketone, methyl butyl ketone, methyl isobutylketone (MIBK), diisobutyl ketone (DIBK), cyclopentanone, cyclohexanone,or a mixture thereof is a particularly preferred solvent. In a furtherembodiment a higher boiling aliphatic, aromatic, or alkylaromatichydrocarbon, or a mixture thereof has proven to be advantageous.Examples of suitable solvents are decane, toluene, xylene,diethylbenzene, naphthalene, tetralin, decalin, and commercial solventmixtures such as Shellsol®, Exxsol®, Isopar®, Solvesso® types, diesel,Solvent Naphtha and/or kerosene. In a preferred embodiment, the solventcomprises at least 10% by weight, preferably 20 to 100% by weight, forexample 30 to 90% by weight, of aromatic constituents. Shellsol® andExxsol® grades are obtainable form Shell and ExxonMobil, respectively.

In a preferred embodiment the major part of the anti-agglomerantformulation is a solvent, and in some cases the anti-agglomerantformulation includes up to 50% by weight of a solvent. In a preferredembodiment a solvent is present in the anti-agglomerant formulation on aweight basis of from 0.01 to 70%, or more preferably from 0.1 to 50%,even more preferably from 0.5 to 30%, and especially preferred from 1.0to 25%. In some embodiments a solvent can be present at from 1.5 to 20%,or from 2.0 to 15%, or from 2.5 to 10%, or even from 5 to 10%.

For example, the anti-agglomerant formulation may contain 10 to 30percent by weight of the N,N-dialkylammoniumalkyl fatty acid amide salt(I) and 70 to 90 percent by weight of a solvent such as methanol. As afurther example, the anti-agglomerant formulation may contain 10 to 30percent by weight of the N,N-dialkylammoniumalkyl fatty acid amide salt(I), 10 to 30 percent by weight of a polymeric kinetic inhibitor, 20 to40 percent by weight of water, and 20 to 40 percent by weight ofethylene glycol.

In a preferred embodiment the composition is essentially free ofglycerol. Essentially free of glycerol means that the compositioncontains less than 1 wt.-%, preferably less than 0.1 wt.-% andespecially preferred no glycerol.

In a further preferred embodiment, agglomeration of gas hydrates isinhibited by injection of a combination of the anti-agglomerants of theformula (I) and optionally (II) together with one or more polymers knownto inhibit the formation and/or agglomeration of hydrates in order tofurther improve the performance of the method according to thedisclosure, as for example to reduce the overall dosage rate. Preferredfurther hydrate inhibitors are polymers having a carbon backbone andamide bonds in the side chains. These include in particular homo- andcopolymers based on vinylpyrrolidone, vinylcaprolactam,isopropylacrylamide, acryloylpyrrolidine, N-acryloylmorpholine,N-acryloylpiperidine and/or N-methyl-N-vinylacetamide, and optionallycontaining further anionic, cationic and neutral comonomers having avinylic double bond, such as for example 2-dimethylaminoethylmethacrylate, 1-olefins, N-alkylacrylamides, N-vinylacetamide,acrylamide, sodium 2-acrylamido-2-methyl-1-propanesulfonate (AMPS) oracrylic acid.

When mixtures of anti-agglomerants according to the disclosure are usedin combination with further polymeric gas hydrate inhibitors, theconcentration ratio between the anti-agglomerants according to thedisclosure of the invention and the mixed-in polymers is preferablybetween 90:10 and 10:90 percent by weight, more preferably between 75:25and 25:75, and especially between 60:40 and 40:60 as for example between90:10 and 25:75, or between 90:10 and 40:60, or between 75:25 and 10:90,or between 75:25 and 40:60, or between 60:40 and 10:90, or between 60:40and 25:75.

Usually such mixtures allow for further reduction of the treat rate ofthe gas hydrate inhibitor according to the disclosure and preferablythey allow for a reduction of the overall dosage rate. When theanti-agglomerants according to the disclosure are used in a mixture withpolymeric gas hydrate inhibitor, the overall concentration of the mixedinhibitors is from 0.01 to 2% by weight or from 0.02 to 1% by weight, inthe aqueous phase to be treated.

In a preferred embodiment agglomeration of gas hydrates is inhibited byinjection of the anti-agglomerants of the formula (I) and optionallyformula (II) together with one or more thermodynamic gas hydrateinhibitors in order to further improve the performance of the methodaccording to the invention, as for example to further reduce the dosagerate of the anti-agglomerant according to formula (I) and optionallyformula (II), to reduce the amount of thermodynamic gas hydrateinhibitor, or to reduce both. While the thermodynamic gas hydrateinhibitor shifts the crystalline equilibrium to lower temperatures theanti-agglomerant according to the disclosure will reduce or even inhibitthe agglomeration of once formed crystallites. Preferred thermodynamicgas hydrate inhibitors are alcohols as for example methanol, ethanoland/or ethylene glycol. The preferred dosage rate of thermodynamic gashydrate inhibitors is between 10 and 60 vol.-% and especially between 20and 50 vol.-% as for example between 10 and 50 vol.-%, or between 20 and60 vol.-% in respect to the aqueous phase to be treated. The preferreddosage rate of the anti-agglomerant according to formula (I) andoptionally formula (II) is as outlined for these anti-agglomerantsabove. However, the dosage rate of at least one of the thermodynamic gashydrate inhibitor and/or the anti-agglomerant according to thedisclosure is lower than its dosage rate required upon its individualuse.

In a further preferred embodiment the fluid to which one or moreanti-agglomerants of the present disclosure is introduced may compriseany number of additional additives. Examples of such additionaladditives include, but are not limited to, salts, surfactants, proppantparticulates, diverting agents, fluid loss control additives, nitrogen,carbon dioxide, surface modifying agents, foamers, corrosion inhibitors,scale inhibitors, wax inhibitors, catalysts, clay control agents,biocides, friction reducers, antifoam agents, flocculants, H₂Sscavengers, CO₂-scavengers, oxygen scavengers, lubricants, viscosifiers,breakers, weighting agents, relative permeability modifiers, resins,wetting agents, and the like. A person skilled in the art, with thebenefit of this disclosure, will recognize the types of additives thatmay be included in the fluids of the present disclosure for a particularapplication

In a preferred embodiment agglomeration of gas hydrates is inhibited byinjection of the anti-agglomerant of formula (I) and optionally formula(II) according to the invention into a wellbore, a subterraneanformation, a vessel, and/or a conduit (and/or into a fluid within any ofthe foregoing) using any method or equipment known in the art. Forexample, agglomeration of gas hydrates may be inhibited by injection ofthe anti-agglomerant into a subterranean formation and/or wellbore usingbatch treatments, squeeze treatments, continuous treatments, and/or anycombination thereof. In certain embodiments, a batch treatment may beperformed in a subterranean formation by stopping production from thewell and pumping an anti-agglomerant formulation into the wellbore,which may be performed at one or more points in time during the life ofa well. In other embodiments, a squeeze treatment may be performed bydissolving the anti-agglomerant in a suitable solvent at a suitableconcentration and squeezing that formulation downhole into theformation, allowing production out of the formation to bring theanti-agglomerant to its desired location. In another preferredembodiment the anti-agglomerant may be injected into a portion of asubterranean formation using an annular space or capillary injectionsystem to continuously introduce the anti-agglomerant into theformation. In all these embodiments the reduced viscosity ofconcentrated solutions of the N,N-dialkylammoniumalkyl fatty acid amidesalt (I) produced by aminolysis of an ester according to the disclosureof this invention allows for a lower pumping pressure and/or a higherconcentration of the N,N-dialkylammoniumalkyl fatty acid amide salt (I)and therefore requires less volume to be pumped.

In a further preferred embodiment a composition (such as a treatmentfluid) comprising the anti-agglomerant according to the presentdisclosure may be circulated in the wellbore using the same types ofpumping systems and equipment at the surface that are used to introducetreatment fluids or additives into a wellbore penetrating at least aportion of the subterranean formation.

Prior to further downstream processing of the valuable hydrocarbonportion of the multiphase fluid the multiphase fluid may be separatedinto its components. Such separation may occur in a separator forexample in a terminal or in a refinery, leaving an aqueous phase fordisposal. The multiphase fluid treated with a N,N-dialkylammoniumalkylfatty acid amide salt (I) produced by aminolysis of an ester accordingto the disclosure of the invention produces a clear water phase withonly little or even no emulsion at the oil-water interface and with onlylittle or even no oil emulsified in the water phase. This allows forfaster separation of the oil and water phases. Furthermore, it enhancesthe productivity of oil and reduces the efforts for disposal of theaqueous phase.

Hydrocarbons in the context of this invention are organic compoundswhich are constituents of mineral oil/natural gas, and their conversionproducts. Hydrocarbons in the context of this invention are alsovolatile hydrocarbons, for example methane, ethane, propane, butane. Forthe purposes of this invention, they also include the further gaseousconstituents of crude oil/natural gas, for instance hydrogen sulfide andcarbon dioxide.

All percent values are given in percent by weight unless otherwisespecified.

EXAMPLES

Materials Used:

For synthesis of the N,N-dialkylammoniumalkyl fatty acid amides thefatty acid esters, N,N-dialkylaminoalkylamines and solventscharacterized in table 1 were used. They were of commercial grades.

TABLE 1 Characterization of reactants used C_(12/14) methyl Mixturecomprising 67% C₁₂ and 21% C₁₄ methyl ester ester; saponification number251 mg KOH/g Coco fatty Methyl ester of coconut oil; C₈-C₁₈ esterpartially acid methyl unsaturated, comprising as main component 46 wt.-%ester C₁₂ saturated fatty acid methyl ester; saponification number 254mg KOH/g Palm kernel Methyl ester of a mixture of C₈-C₁₈ fatty methylester acids, comprising as main components 48 wt.-% C₁₂ saturated fattyacid methyl ester and 13 wt.-% C₁₈ mono-unsaturated fatty acid methylester; saponification number 241 mg KOH/g C_(8/10) acid Methyl ester ofa mixture of fatty acids, containing as methyl ester main components 83%C₈ and C₁₀ essentially saturated fatty acid methyl esters;saponification number 324 mg KOH/g Methyl Methyl ester of oleic acid(technical grade having 74% oleate purity, further comprising stearicacid and linoleic acid); saponification number 188 mg KOH/g CoconutTriglyceride of C₈-C₁₈ fatty acids, comprising as oil main components45% C₁₂ saturated fatty acid and 9% unsaturated fatty acids. Free fattyacids content 1%. DBAPA N,N-Dibutylamino propyl amine (≥98%) DMAPAN,N-Dimethylamino propyl amine (>98%) MSA methane sulfonic acid SolventMixture of aromatic hydrocarbons having carbon Naphtha numberspredominantly in the range of C₉ through (SN) C₁₁ and boiling in therange of from 177° C. to 216° C.

Saponification numbers were determined according to DIN/EN/ISO 3681.

Starting from the raw materials characterized in table 1 theN,N-dialkylammoniumalkyl fatty acid amides were produced according tothe following general procedure:

A 4-necked flask, equipped with a Dean-Stark apparatus, overheadstirrer, thermometer and nitrogen-purging line was charged with thefatty acid ester, the N,N-dialkylaminoalkylamine, and 0.5 wt.-% ofsodium methoxide. The mixture was heated to 140-180° C. for a period of6 to 12 hours. The alcohol liberated during aminolysis was distilledoff. The conversion was monitored by amine value distribution titration;the reaction was stopped when the primary amine value was <6 mg KOH/g.For the comparative examples (using a triglyceride) the reaction wasstopped when a primary amine number of less than 15 mg KOH/g wasobtained.

Following the aminolysis reaction the reaction product was cooled tobelow 80° C. and diluted with a solvent (methanol or solvent naphtha).Subsequently the organic acid was added in such a manner that thetemperature of the reaction mixture did not exceed 50° C. to form thefinal N,N-(dialkylammoniumalkyl)carboxylic acid amide salt. Details ofthe various syntheses are given in table 2.

TABLE 2 Reactants and reaction pathways for the preparation ofN,N-dialkylaminoalkyl fatty acid amides (II) andN,N-(dialkylammoniumalkyl)carboxylic acid amide salts (I)N,N-dialkylaminoalkyl fatty acid amide (II) Ammonium salt (I) SolutionAmmonium fatty acid N,N-dialkylamino- molar ratio carboxylic molar ratioactive salt ester (IV) alkylamine (V) (IV):(V) acid (VI) (II):(VI)solvent concent AS 1 C_(8/10) methyl ester DBAPA 1:1 acrylic acid 1:1methanol 85% AS 2 C_(12/14) methyl ester DBAPA 1:1 acrylic acid 1:1 SN85% AS 3 methyl cocoate DBAPA 1:1 acrylic acid 1:1 methanol 60% AS 4palm kernel methyl DBAPA 1:1 acetic acid 1:1 ethylene 60% ester glycolAS 5 methyl oleate DMAPA 1:1 acrylic acid 1:1 methanol 60% AS 6 coconutoil DBAPA 1:1 acrylic acid 1:1 methanol 85% (comp.) AS 7 coconut oilDBAPA 1:1 acrylic acid 1:1 SN 85% (comp.) AS 8 Coconut oil DBAPA 1:1acetic acid 1:1 methanol 60% (comp.) AS 9 C_(12/14) acid methyl DBAPA1:1 MSA 1:1 SN 60% (comp.) ester

The dynamic viscosities of the samples according to table 1 weredetermined by using a rheometer from Anton-Paar at the given temperatureat a shear rate of 106·s⁻¹. The results are given in table 3.

TABLE 3 Viscosities of the N,N-(dialkylammoniumalkyl)carboxylic acidamide salts measured in different solvents N,N-(dialkyl- ammoniumalkyl)Exam- carboxylic active Viscosity Viscosity ple acid amide salt solventcontent @10° C. @20° C. 1 AS 3 methanol 60% 1 <1 2 AS 4 methanol 60% 2<1 3 AS 5 methanol 60% 1 <1 4 AS 9 SN 60% 148 86 (comp.) (comp.) 5 AS 8methanol 60% 22 5 (comp.) (comp.) 6 AS 1 methanol 85% 153 101 7 AS 6methanol 85% 295 144 (comp.) (comp.) 8 AS 2 SN 85% 466 218 9 AS 7 SN 85%835 365 (comp.) (comp.)

For evaluation of the performance of the presently disclosedN,N-dialkylammoniumalkyl fatty acids amide salts (I) as low dose gashydrate inhibitors, a rocking cell test was used. The rocking cell testis a commonly used test in the art for assessing the performance ofanti-agglomerant chemistry. Briefly, additives are evaluated based ontheir ability to effectively minimize the size of hydrate particleagglomerates and then to disperse those particles into the hydrocarbonphase. The results were classified as “pass” or “fail” based on whetherhydrate blockages were detected. Performance is evaluated by determiningthe minimum effective dose (MED) required to register as a “pass” in therocking cell test. The effective dosages (MEDs) were screened for 5.0wt.-% NaCl brine at 50 vol.-% watercut and 138 bar at 4° C.

The rocking cell apparatus (“rack”) is comprised of a plurality ofsapphire tubes, each placed within a stainless-steel support cage. Eachassembled sapphire tube and steel cage (hereby referred to as a rockingcell) is typically loaded with a fluid containing a hydrocarbon phaseand a brine phase, along with a stainless-steel ball for mixing. Therocking cell can withstand pressures of up to 200 bar (2900 psi). Therocking cell, once loaded with the fluids, is then mounted on the rackwith gas injection and pressure monitoring. During testing, as the gasescooled, and hydrates formed, the consumed gas was substituted via ahigh-pressure syringe pump to maintain the system at constant pressure.

The rack was loaded with 10 rocking cells in a 2×5 configuration (twocells wide and 5 cells tall). The center position on the rack (betweentwo cells) was fixed and allowed to rotate while the outer positions onthe rack were moved vertically up and down. This vertical motion allowedthe rocking cells to rotate into a positive or negative angle position.The steel ball placed inside the sapphire tube moved from one end of thecell to the other during a rocking motion. The rack rocked up and downat a rate of about 5 complete cycles (up and down) every minute. Therack was further contained within a temperature-controlled bath attachedto a chiller with temperature control from −10° C. to 60° C.

The rocking cells were filled with three components: hydrocarbon,aqueous phase, and gas. First, each rocking sapphire tube was filledwith 5 ml of dodecane and a 5 ml of 5% NaCl brine (water cut 50 vol.-%)for a total liquid loading of 50% total tube volume (20 ml total). Theanti-agglomerants according to table 2 were added at dose rates inpercent, by volume of water (vol.-%). Green Canyon gas was used for thistesting with its composition given in Table 4.

TABLE 4 Green Canyon gas composition Component Name Chemical SymbolAmount (mol) Nitrogen N₂ 0.14 Carbon Dioxide CO₂ 0 Methane C₁ 87.56Ethane C₂ 7.6 Propane C₃ 3 i-Butane i-C₄ 0.5 n-Butane n-C₄ 0.8 i-Pentanei-C₅ 0.2 n-Pentane n-C₅ 0.2

Rocking Cell Test Procedure:

-   -   A. Pretest Steps: Once the rack has been loaded with the rocking        cells containing hydrocarbon fluid, brine and the        anti-agglomerant, the rocking cells are evacuated with a vacuum        pump for 15-20 minutes. While evacuating, the bath temperature        is increased to the starting test temperature of 49° C. Once the        bath has reached 49° C., the cells and the syringe pump are        pressurized with Green Canyon gas to 138 bar and the syringe        pump is switched on to maintain pressure during initial        saturation.    -   B. Saturation Step: The apparatus is set to rock at 5 rocks per        minute for 2 hours to ensure the hydrocarbon fluids and brine        loaded in the cell have been saturated with gas. This testing is        performed at constant pressure and the syringe pump remains        switched on and set at 138 bar for the remainder of the test.    -   C: Cooling Step: While maintaining a rocking rate of 5 rocks per        minute, the system is cooled from 49° C. to 4° C. over 6 hours.    -   D. Steady State Mixing Step before Shut-in: At the constant        temperature of 4° C., the apparatus is kept rocking at 5 rocks        per minute for 12 hours to ensure complete hydrate formation.    -   E. Shut-in Step: The apparatus is set to stop rocking and to set        the cell position to horizontal and kept at a constant        temperature of 4° C. for 12 hours.    -   F. Steady State Mixing Step after Shut-in: At the conclusion of        the shut-in period, the apparatus is restarted at the rate of 5        rocks per minute at the constant temperature of 4° C. for 4        hours.    -   G. Test Completion: At the conclusion of the experiment, the        apparatus is set to stop rocking and the cells are set at a        negative inclination to keep fluids away from the gas injection        port. The chiller bath is set to 49° C. to melt any formed        hydrates and allow for depressurization and cleaning.

To determine the relative performance of each inhibitor or dose rate ofinhibitor, visual observations were made during the steady state mixingstep after shut-in (period F) and correlated with an interpretation ofthe time required for the ball within the cell to travel between twomagnetic sensors. Each experiment was conducted in duplicate to confirmreproducibility. Table 5 below shows the results (average values) of therocking cell tests.

TABLE 5 Test results as anti-agglomerant in rocking-cell tests AmmoniumMinimum Effective Dose Rate Test salt (wt %, based on water cut) 10 AS 10.35% 11 AS 2 0.35% 12 AS 3 0.45% 13 AS 4 0.55% 14 AS 5 0.55% 15 AS 1 +0.40% AS 3 (1:1) 16 AS 6 0.70% (comp.) 17 AS 8 0.75% (comp.) 18 AS 90.90% (comp.)Testing of Water Quality Upon Phase Separation of Gas and Fluid Phase

For assessment of the water quality obtained upon depressurization andseparation of the gas form hydrocarbon and aqueous phase, samples (25resp. 45 ml) of the crude oils characterized in table 6 where filledinto graduated 120 ml glass bottles and filled to 100 ml with tap water.The bottles were placed in a heating bath of 100 F (37.8° C.) for 1hour. Afterwards, the amount of anti-agglomerant given in tables 7 and 8was added and the bottles where combined in a box and shaken 200 times.Afterwards, the bottles were placed again in the heating bath. The waterseparation (measured in mL) and the water quality were rated after 5 minand 120 min of incubation time. Water quality was rated visually usingthe following grading:

-   -   water quality: 1=Clear and bright        -   2=Slight Haze        -   3=Hazy        -   4=Opaque

TABLE 6 Characterization of test oils Oil A Oil B API gravity 30.9°21.8° Saturates 23.11% 27.82% Aromatics 32.36% 54.71% Resins 35.08%14.50% Asphaltenes 7.27% 2.97%

The oils were further characterized by their contents of saturates,aromatics, resins and asphaltenes. The SARA analysis was made using alatroscan TLC-FID according to standard method IP 469.

As can be recognized from the test results, the method usingN,N-dialkylammoniumalkyl fatty acid amide salts produced by aminolysisof a N,N-dialkylaminoalkylamine with a fatty acid ester according to theinvention requires lower additive dosage rates than comparable methodsaccording to the state of the art. Furthermore, the reduced viscosity ofthese amide salts eases application to the fluid to be treated.Additionally, the method allows for an improved water quality upon phaseseparation. These are distinct improvements over the prior art.

TABLE 7 Test results on water quality in Oil A Water/oil (75:25 vol.-%)Water/oil (55:45 vol.-%) Ammonium Dosage water separation water qualitywater separation water quality Test salt [wt.-%] 5 min 120 min. 5 min120 min. 5 min 120 min 5 min 120 min 19 AS 1 0.5 51 ml 70 ml 1 1 42 ml51 ml 1 1 20 AS 1 1.0 55 ml 71 ml 1 1 43 ml 52 ml 1 1 21 AS 2 0.5 53 ml73 ml 1 1 45 ml 51 ml 1 1 22 AS 2 1.0 58 ml 69 ml 1 1 38 ml 53 ml 1 1 23AS 5 0.5 59 ml 71 ml 1 1 40 ml 52 ml 1 1 24 AS 5 1.0 59 ml 71 ml 1 1 43ml 53 ml 1 1 25 AS 6 0.5 44 ml 65 ml 3 2 40 ml 50 ml 1-2 1 (comp.) 26 AS6 1.0 47 ml 68 ml 3 2 35 ml 45 ml 2-3 1-2 (comp.) 27 AS 9 0.5 40 ml 59ml 3 3 37 ml 46 ml 2 1-2 (comp.) 28 AS 9 1.0 42 ml 63 ml 4 3 31 ml 41 ml3 2 (comp.)

TABLE 8 Test results on water quality in Oil B Water/oil (75/25 vol.-%)Water/oil (55/45 vol.-%) Ammonium Dosage water separation water qualitywater separation water quality Test salt [wt.-%] 5 min 120 min. 5 min120 min. 5 min 120 min 5 min 120 min 29 AS 1 0.5 43 ml 59 ml 3 1 20 ml25 ml 1 1 30 AS 1 1.0 50 ml 60 ml 2 1 23 ml 32 ml 2 1 31 AS 1 2.0 54 ml65 ml 2 1 27 ml 38 ml 2 1 32 AS 3 0.5 41 ml 55 ml 2 1 18 ml 23 ml 1 1 33AS 3 1.0 48 ml 59 ml 2 1 22 ml 26 ml 2 1 34 AS 3 2.0 52 ml 63 ml 3 1 25ml 30 ml 2 1 35 AS 4 0.5 40 ml 57 ml 2 1 20 ml 25 ml 1 1 36 AS 4 1.0 45ml 62 ml 2 1 22 ml 27 ml 1-2 1 37 AS 4 2.0 40 ml 63 ml 3 1 25 ml 31 ml 21-2 38 AS 6 0.5 40 ml 50 ml 4 2 n.d. 20 ml 4 2 (comp.) 39 AS 6 1.0 45 ml52 ml 3 2 n.d.  5 ml 4 3 (comp.) 40 AS 6 2.0 42 ml 49 ml 4 3 n.d.  5 ml4 3 (comp.) n.d. = not detectable

The invention claimed is:
 1. A method for inhibiting the agglomerationof gas hydrates, comprising the step of injecting at least oneanti-agglomerant comprising at least one N,N-dialkyl-ammoniumalkyl fattyacid amide represented by the formula (I)

wherein R¹ is an alkyl or alkenyl group having from 7 to 21 carbonatoms, R² and R³ are each independently an alkyl group containing 1 to10 carbon atoms, or together form an optionally substituted ring having5 to 10 ring atoms, wherein the ring may carry up to 3 substituents, R⁴is hydrogen or an alkyl group having 1 to 6 carbon atoms, R⁵ is hydrogenor an optionally substituted hydrocarbyl group having 1 to 22 carbonatoms and A is an alkylene group having two or three carbon atoms, intoa fluid comprising gas, water and oil under conditions prone to theformation of gas hydrates, wherein the at least oneN,N-dialkyl-ammoniumalkyl fatty acid amide represented by formula (I) isproduced by the aminolysis of a fatty acid ester of at least one fattyacid and at least one monohydric C₁ to C₄-alcohol with at least oneN,N-dialkylamino alkyl amine and subsequent neutralization with at leastone carboxylic acid, wherein the fatty acid ester of the at least onefatty acid with the at least one monohydric C₁-C₄-alcohol has theformula (III)R¹—COOR⁶  (III) wherein R¹ is defined above, and R⁶ is an alkyl grouphaving 1 to 4 carbon atoms, and wherein the at least oneN,N-dialkylamino alkyl amine has the general formula (V)

wherein R², R³, R⁴ and A are each independently defined above.
 2. Themethod according to claim 1, wherein R¹ is an alkyl or alkenyl grouphaving 12 or 14 carbon atoms.
 3. The method according to claim 1,wherein at least 60 mol-% of the at least one fatty acid has 12 to 14carbon atoms.
 4. The method according to claim 2, wherein the molarratio of the fatty acid having 12 carbon atoms and the fatty acid having14 carbon atoms is between 1:9 and 9:1.
 5. The method according to claim1, wherein R¹ is a linear alkyl or alkenyl group having from 7 to 21carbon atoms.
 6. The method according to claim 1, wherein the at leastone monohydric C₁-C₄-alcohol is selected from the group consisting ofmethanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol,tert.-butanol and mixtures thereof.
 7. The method according to claim 1,wherein the at least one fatty acid and the at least oneN,N-dialkylaminoalkylamine are reacted in a molar ratio of between 3:1and 1:3.
 8. The method according to claim 1, wherein the at least onecarboxylic acid is selected from the group consisting of formic acid,acetic acid, propionic acid, butyric acid, pivalic acid, hexanoic acid,octanoic acid, 2-ethyl hexanoic acid, decanoic acid neodecanoic acid,undecanoic acid, neoundecanoic acid, dodecanoic acid, neododecanoicacid, tridecanoic acid, iso-tridecanoic acid, tetradecanoic acid,hexadecanoic acid, octadecanoic acid, acrylic acid, methacrylic acid andmixtures thereof.
 9. The method according to claim 1, wherein the atleast one fatty acid and the at least one carboxylic acid are different.10. The method according to claim 9, wherein the at least one fatty acidand the at least one carboxylic acid differ in at least one parameter,wherein the parameter is selected from the group consisting of alkylchain length, acid value, degree of branching, and degree ofunsaturation.
 11. The method according to claim 1, wherein the at leastone anti-agglomerant is essentially free of glycerol.
 12. The methodaccording to claim 1, wherein the at least one anti-agglomerant isinjected into the fluid prone to the formation of gas hydrates prior toformation of hydrates.
 13. The method according to claim 1, wherein thecompound according to formula (I) is combined with at least onepolymeric gas hydrate inhibitor.
 14. The method according to claim 1,wherein the compound according to formula (I) is combined with at leastone thermodynamic gas hydrate inhibitor.
 15. The method according toclaim 1, wherein the fluid has a pH value of below 8.0.